In complex electrical systems such as computers it is common to use power and grounding bus bars or rails. Often these bus bars have hundreds or even thousands of wires connected thereto. After the wires are attached to the bus bars and the circuits are inspected, shorts are invariably discovered, especially when the terminals are closely spaced. It is very difficult and time consuming to detect these wiring errors. If the system is energized before shorts are removed, components in the system can be damaged.
In the past, searches for shorts were normally conducted after the electrical equipment was completed, not during the actual assembly process. Often an ohmmeter was used to hunt for shorts.
Some test instruments have been designed to detect shorts in assembled cables. They require a connector for each end of the cable under test and they utilize complex circuits, slow unreliable mechanical switching devices, or high voltages. Representative cable testing devices are disclosed in U.S. Pat. Nos. 2,814,774; 3,480,856; and 4,015,200.
U.S. Pat. No. 3,713,019 describes an apparatus for sequentially examining points in an electrical matrix so as to detect failures in components such as transistors. A transformer is required at every sensing station and the switching is accomplished with relays.